Pattern materials



Patented May 10, 1949 airman MATERIALS Kenneth E. Rose, Columbus, Ohio, assignor, by

mesne assignments, to Uni ted Aircraft 1 Corporation, East Hartford, Conn., a corporation of Delaware No Drawing. Application March 2:, 1946,

Serial No. 658,777

3 Claims. (Cl. 22-164) 1 This invention relates to particularly to pattern materials especially suitable for precision investment-casting processes;

In the precision investment-casting process, a

, pattern is cast in a pattern mold and an investment material is cast around the pattern. The investment mold thus formed is then heated and the pattern is removed, as by melting, burning, volatilization, or chemical decomposition, leaving the desired cavity in the mold. It has been the customary practice to make the patterns from wax or wax-like materials, since they may be readily removed at relatively low temperatures. The principal use of precision investment-casting was, in its early stages, in the dental industry where the pattern material had to melt at temperatures only slightly above body temperature and solidify at body temperature due to its use in the mouth of the patients. Subsequent advances in the precision investment-casting art have widened the use of this type of casting, and it is now used in. many other fields, for example, in casting blades for turbo-superchargers for aircraft engines.

Although there is little information as to particular pattern materials which are especially suitable for precision investment-casting,the requirements of such materials are critical and well known in the art. In the first place, it is essential that the.

pattern material be capable of reproducing with great accuracy the contours of the pattern mold. In order to achieve such reproducibility, it is desirable to have low thermal expansion, low viscosity of pattern material when molten, fine grain structure, and a pattern material of crystalllne nature. Secondly, it is desirable that the pattern material be characterized by sufiicient strength and resilience to prevent cracking of the pattern when cast in a mold ofiering resistance to shrinkage. Furthermore, the pattern material should be hard and have very little, if any, cold flow in order that the pattern will not materially alter in contour from the time it is cast until the time the investment is cast around it. Finally, it is highly important that the pattern material be characterized by uniform shrinkage regardless of the temperature at which it is poured. The present casting waxes and other pattern materials have failed to fulfill these requirements and, as a result, the employment of precision investment-casting processes has been generally restricted to small castings, thus eliminating the production of many of the more important products which might be precision made.

It is, therefore, an object of this invention to provide a pattern material capable of highly acpattern materials and molds of intricate design which offer resistance to the shrinkage of the pattern material.

, and the time that the investment is cast about Q curate reproduction of the contours of the pat- Y tern mold.

Another object of this invention is to provide a pattern material that may be readily cast in becomes clearly noticeable in It is a further object of this invention to provide pattern materials characterized by considerable cold flow stability and hardness so as to prevent distortion between the time of molding the pattern.

Still another object of this .invention is to provide a pattern material characterized by uniform shrinkage regardless of the temperature at which the. pattern material is poured.

Yet another object of this invention is to provide a pattern material satisfactory for casting large objects with the precision investment-casting method.

Other objects and advantages of the present invention will become apparent from the following detailed description thereof.

The present invention comprises, in general, a pattern material consisting essentially of a mixture of hydrogenated castor oil and chlorinated naphthalene in certain proportions. Neither or these two materials by itself is satisfactory as a pattern material; the hydrogenated castor oil has very poor castability because of its brittleness and the chlorinated naphthalene has such a large grain structure that it does not reproduce the contours of the pattern mold with sufficient accuracy. When mixed together, these two compounds do not generally produce a satisfactory pattern material, but it has been discovered that those mixtures containing between about 60 and about chlorinated naphthalene and between to are employed in precision investment-casting processes wherein the accuracy of reproduction is generally the sole justification for the greatly added cost of casting metal in this manner. Since mixtures of hydrogenated castor oil and chlorinated naphthalene containing frcm about 60 to about 80% chlorinated naphthalene have very low viscosity when molten, they readily reproduce the contours of the mold. The principal limitation on the reproductive qualities of such mixtures is the growth of grain size which compositions containing much more than 80% chlorinated naphthalene.

Not only are such mixtures of chlorinated naphthalene and hydrogenated castor oil capable of. reproducing the contours of the pattern mold, but they are exceptionally castable, that is, they are characterized by sufllciently low thermal expansion, high strength, and resilience to prevent cracking of the pattern from cooling in intricate molds which present considerable resistance to shrinkage. In the following Table 1, the per cent of volumetric thermal expansion which occurs upon heating the pattern material from 20 C. to its melting point is shown for various mixtures of hydrogenated castor oil and chlormated naphthalene (49% chlorine).

Table 1 d N h hal iii lfi i -Chlori to a t ene er Hydrogenated Castor Miilxtum na p Expansion percent 30% chlorinated 40 7 chlorinated 50 0 chlorinated 60% chlorinated 75% chlorinated 80% chlorinated 90% chlorinated The fact that the peak of thermal expansion lies at about 50% chlorinated naphthalene accounts, at least in part, for the rapid decrease in castability of compositions containing less than 60% chlorinated naphthalene. This lower limit is further established by the embrittling action encountered in compositions containing in excess of 40% hydrogenated castor oil. Statistical afllrmation of this observed result is found in the following Tables 2 and 3, which show, respectively, the relative transverse strength and the deflection of diflerent mixtures of hydrogenated castor oil and chlorinated naphthalene (49% chlorine).

Table 2 Transverse H dr enated Castor Oil-Chlorinated Naphthalene y 0g Mixture 2x53? The transverse strength of a given pattern material is determined by suspending a weight at the middle of a bar of the pattern material having a cross-section of x inch and a span of 3 inches. The deflection is measured directly below the point of application of the load, and represents the ability of the pattern material to bend before breakage occurs. a

It is apparent from the above Tables 2 and 3 that both the transverse strength and the resilience, or deflection, of the hydrogenated castor oil-chlorinated naphthalene mixtures decrease for certain purposes.

markedly below 60% chlorinated naphthalene.

As a result, the lower limit of 60% chlorinated naphthalene not only marks the point below which successful casting of these waxes becomes '4 extremely diflicult, but also indicates a limit below Mixtures of hydrogenated castor oil and chlorinated naphthalene containing as high as 90% of the latter have suitable properties for pattern materials, but the use of such compositions containing in excess of chlorinated naphthalene is impractical. The is to employ chilled molds for forming patterns in orderto reduce the time required for cooling the pattern material and, consequently, reducing the molding period. Due to the rise in melting point of mixtures containing more than 80% chlorinated naphthalene, the temperature diiferential between such mixtures and the chilled molds results in cracked patterns. Patterns may be cast satisfactorily, however, using compositions containing up to chlorinated naphthalene if the molds are warm, and even where the molds are cold it the pattern is quite large so that the chilling effect is minimized.

The hydrogenated castor oil used is principally a 12-hydroxy stearin (glyceryl trihydroxy stearate). The chlorinated naphthalene employed can vary in degree of chlorination between naphthalene trichloride and naphthalene hexachloride. The chlorination of naphthalene results in a product comprising a mixture of different chlorides, so that it is more practical to define this product according to chlorine content, density, melting point, etc. Thus, chlorinated naphthalene having a chlorine content of about 49% and having a melting point of about 80 C. has been I found to be very satisfactory, and another chlorinated naphthalene having a chlorine content as high as 61% has been found to be even better may be reduced to as low as 50% and still provide satisfactory pattern materials. A mixture which has been found to be especially advantageous when using any of the chlorinated naphthalenes containing chlorine within the range of about 49% to about 61 comprises about 25% hydrogenated castor oil and about 75% chlorinated naphthalene. A

The chlorinated naphthalene being actually a mixture of several compounds. does not form a true binary system with the hydrogenated castor oil so as to permit accurate predictions of melting points, freezing points, and other physical properties, from the properties of the previously known mixtures of these two compounds. Consequently, the discovery that compositions of hydrogenated castor oil and chlorinated naphthalene containing from about 60 to about 80% chlorinated naphthalene were particularly adapted present commercial practice for use as pattern materials was an unpredictable development.

In summary, the present invention lies in the discovery that a relatively narrow range of the mixture of hydrogenated castor oil and chlorinated naphthalene may be employed satisfactorily as pattern materials, but mixtures falling within this range, indicated for most purposes by those mixtures containing between 60 to 80% chlorinated naphthalene, have excellent properties which especially suit them for production of patterns. Such materials have a very high degree of accuracy of reproduction and may be readily cast in the most intricate molds. Upon removal from the pattern mold, patterns made of the mixtures comprising the present invention will retain their dimensions within very close tolerances over long periods of time. The extremely low viscosity of the molten hydrogenated castor oil-chlorinated naphthalene mixtures makes it possible to gravity cast as well as to injection mold the patterns. This latter feature is of especial importance in that a considerable saving is realized by elimination of highly expensive mechanisms required for molding under pressure.

Another characteristic of especial importance of the present pattern materials is the uniform shrinkage obtained regardless of the pouring temperature. High dimensional accuracy of the part to be molded by precision casting is generally required, so that it is necessary to allow for even slight shrinkage of the pattern upon cooling. This can be done satisfactorily on a commercial basis only where the shrinkage is uniform regardless of slight variations, or even large variations. in the pouring temperature. Still another factor of considerable commercial importance is the reduced cost of the present pattern material when compared with pattern materials heretofore in general use. Still another feature is the excellent machinability of this pattern material which permits drilling, threading. or turning to provide features that might be difllcult to incorporate in a pattern mold.

A number of variations of the present invention will become apparent to those skilled in the art upon reading this disclosure, and such variations or modifications as fall within the appended claims constitute a part of the present invention.

What is claimed is:

1. A pattern material consisting essentially of a mixture of hydrogenated castor oil and chlorinated naphthalene in which the latter compound is present in the mixture to the extent of from about to about 90% and has a chlorine content of about 49% to about 60%.

2. A pattern material consisting essentially of a mixture of hydrogenated castor oil and chlorinated naphthalene, said mixture containing about 60% to about 80% of chlorinated naphthalene which has a chlorine content of about 49% to about 61%. Y

3. A pattern material consisting essentially of about 25% hydrogenated castor oil and about chlorinated naphthalene having a chlorine content of from 49% to about 61%.

KENNETH E. ROSE.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,133,300 Linebarger et al. Oct. 18, 1938 2,266,813 Ruben Dec. 23, 1941 OTHER REFERENCES The Foundry, page 184, Wax Compositions,

40 April 1944. 

